"We once had a client who had a pottery vase they were using as a toilet brush holder," says Stuart Whitehurst, vice president of Skinner, Inc. auctioneers in Boston. "They had no idea it was made in the late 1800s by Boston pottery maker William Grueby and that its yellow glaze was extremely rare. That toilet brush holder ended up being worth $18,000." So how do you know if Grandma's umbrella stand is actually precious pottery? JustArtPottery.com has a large gallery of patterns and frequently publishes articles on how to tell what kind of pottery you own. And one of the hottest items on the market right now, Whitehurst says, is Chinese porcelain. Commonly found in a traditional blue and white motif, it's now exceptionally popular because Chinese collectors are trying to reclaim pieces that were brought to the States by American missionaries in the 20th century.